1. Field of the Invention
The present invention relates to a quartz thin film for use in vibrators, oscillators, high frequency filter surface acoustic wave elements, optical waveguides, semiconductor substrates and the like, and to a production method therefor.
2. Description of the Related Art
Quartz thin films have been widely used for vibrators, oscillators, high frequency filter surface acoustic wave elements, optical waveguides and the like, and are very important industrial materials. Quartz thin films are produced by a method in which a single crystal of quartz obtained by a hydrothermal synthesis is polished to provide a thin film, or by a direct production method such as a sol-gel method, a plasma enhanced chemical vapor deposition (CVD) method, a sputtering method, and a laser ablation method.
Many thin film techniques for single crystals of quartz have been developed, as disclosed in Japanese Unexamined Patent Applications, Publication Nos. 8-157297, 8-225398, 8-268718, 8-91977, and 9-315897.
In these patent publications, a single crystal of quartz thin film is produced by a sol-gel method, a plasma CVD method, or a sputtering method using a silicon alkoxide as a source material. The sol-gel method requires many complex steps such as adding alcohol, water, and amine to a source solution, refluxing, coating on the substrate, drying, and heat processing. The plasma CVD method, the sputtering method, and the laser ablation method require large-scale equipment. For example, in the laser ablation method, a sintered target is irradiated with an ultraviolet laser pulse under an ultra-high vacuum to vaporize it and produce a plasma, thereby growing a thin film on a substrate. It requires a vacuum device capable of reducing pressure to an extreme degree, an eximer laser, and a sintered material. The growth rate of the quartz thin film formed on the substrate is as low as 0.25 μm/h.
In summary, the sol-gel method requires many steps and is therefore unsuitable for industrial production. The laser ablation method requires expensive equipment, such as vacuum devices, and expensive materials such as highly purified silicon dioxide as a target, and can grow a quartz thin film only at a low rate, which makes it unsuitable for industrial production.